Distillation apparatus

ABSTRACT

A novel one-piece tray and matching supporting ring simplify the assembly of distillation columns having multiple plates. The trays and the openings in their supporting rings, which are attached to the inner wall of the column, are in the shape of a circle interrupted by two parallel chords, the tray width between the tray chords being smaller than the circular diameter of the ring opening.

This invention concerns a distillation column having multiple plateswith trays shaped to facilitate column assembly.

Distillation columns are widely used in the chemical processing industryfor the fractionation and separation of liquid mixtures. Typical usesinclude the refining of oil, recovery of solvents from industrialoperations, and the separation of volatile organic compounds from steam.Most of these columns use multiple plates to increase fractionationefficiency. The bubble cap fractionating column has been a particularfavorite.

The column may be constructed of several segments, called spool pieces,stacked atop each other and bolted together to reach the desired height.Each spool piece may contain one or more plates. A plate consists of atray and its support. The trays are peripherally supported and spacingmaintained inside the column by supporting rings on the interior of thespool pieces. When more than two plates are fitted within a singlecolumn or spool piece, assembly thereof becomes difficult because awhole tray cannot be passed through the support rings from one trayposition to another. The usual assembly technique requires making thetray in two halves, inserting the halves separately, and assembling thetray inside the spool piece. The assembled tray must be leakproof tomaintain a liquid pool on its surface. Therefore the joints, where thetray pieces mate to form a complete tray, require backup plates,gaskets, and closely-spaced bolting. This assembly is cumbersome andexpensive. The use of assembled trays can be avoided by using only twoplates per spool piece, but this results in an economic penalty becausethe connecting flanges of each spool piece must be carefully machined tobe smooth and flat, properly gasketed, and bolted for a liquid and vaporproof seal. The most economical column assembly would have relativelylong spool pieces with several plates each, if it were not for theproblem of assembling trays inside the long spool pieces.

This invention is in a distillation column containing more than twodistillation plates, each plate being comprised of a circular trayperipherally supported by a ring attached to the inner cylindrical wallof the column, and the supporting ring having an opening, theimprovement comprising said tray periphery and said opening both havingthe shape of a circle interrupted by two parallel chords, and the traywidth between the tray chords being smaller than the circular diameterof the support ring opening.

Preferably for simplicity the tray chords equal each other in length andthe ring opening chords are equal. To peripherally support the tray, thecircular diameter of the ring opening must be smaller than the circulardiameter of the tray and the opening width between chords must besmaller than the tray width between chords. When assembled, the traychords are preferably oriented substantially parallel to the ringopening chords.

FIG. 1 shows a top view of tray 10 having a periphery consisting ofcircular portions 12 interrupted by parallel chords 14. The traycontains the necessary openings and fittings (not shown) for assemblyand use in a distillation column.

FIG. 2 is the top view of a tray support ring 20 having a circularperiphery 22 and an opening 24 in the shape of two circular portions 26interrupted by two parallel chords 28.

FIGS. 3 through 6 illustrate in sequence how a tray may be passedthrough support rings mounted in a cylindrical distillation column spoolpiece and positioned for assembly at the desired location. The arrowsindicate the direction of movement of vertically oriented tray 10through spool piece 30. As shown in FIG. 4, tray 10 is dimensioned sothat the tray width between tray chords 14 is smaller than the circulardiameter of the opening in ring 20. When the desired tray location isreached, as shown in FIGS. 5 and 6, tray 10 is tilted to a horizontalposition, turned and set on ring 20 so that the chords 14, or flatsides, of the tray are in a substantially parallel relationship withthose of the corresponding support ring so that a liquid-tight joint canbe made.

The new tray design permits the use of one piece trays in spool pieceswhich contain more than two plates. The trays are circular except thaton two sides, at 180° to each other, the circular form has been reducedto form flat edges (chords). The length of each chord can be about 0.4times the outer diameter of the circular part of the tray.

The length of the tray chord is a function of the tray circular diameter(OD), the clearance desired beween the tray chords and the circularinside ring diameter (CL), and the overlap required to seal the tray tothe support ring (OL). As an example, a tray with a circular diameter of22 30/32 in. (58.26 cm), a tray-to-ring overlap of 1 1/32 in. (2.62cm.), and a tray-to-ring assembly clearance of 4/32 in. (0.32 cm.),would require a ring diameter (ID) of 20 28/32 in. (53.02 cm.). Thedistance from tray center to tray chord would be 10 10/32 in. (26.19cm.). A general expression can be derived. Tray center to tray chord=CF= 1/2(OD)-. OL-CL. Length of the tray chord = TF= 2 √(OD)² /4- (CF)² =√(OD)² - 4(CF)². This can be rewritten as: TF= √(OD)² - 4[(OD/.sub. 2-OL-CL)]² = √(OD)² - [OD-2(OL + CL)]².

This tray and tray support permits the use of one piece trays in spoolpieces containing more than two plates per piece. The new trays are lesscomplex, have fewer parts, and make assembly and disassembly ofdistillation column easier.

What is claimed is:
 1. In a distillation column having a cylindricalwall and containing more than two distillation plates, each plate beingcomprised of a circular tray peripherally supported by a ring attachedto said inner cylindrical wall of the column, and the support ringhaving an opening, the improvement comprising said tray periphery andsaid opening both having the shape of a circle interrupted by twoparallel chords, the tray width between the tray chords being smallerthan the circular diameter of the support ring opening.
 2. The apparatusof claim 1 wherein the lengths of the tray chords are equal and thelengths of the ring opening chords are equal.
 3. The apparatus of claim2 wherein the tray chord length is about 0.4 times the circular diameterof the tray.